Of course there are commercial products available for this type of application like the the WiFi-502 from Measurement Computing Corporation as seen in the first image. This product is priced at $185 per unit which greatly exceeds the stated criteria of being cheap (eg no more than $20/unit). While it meets the criteria of monitoring Temp & Humidity and wireless transmission of data to a local PC, that data would not be automatically transmitted to the project management team.

Because the "Citizen Scientist" participation in this project involves collecting samples from household surfaces and participants are provided with test sample collecting materials, I propose the following:

Provide a low-cost digital thermometer/hygrometer with the sample collecting materials.

Add the step of taking temp & humidity readings as part of the data collecting process.

Use a free web-based "office" software suite such as Google Drive to create a form that participants use to input their climate data which will be logged in spreadsheet format for immediate project management monitoring and future analysis.